leetcode 53. Maximum Subarray

Find the contiguous subarray within an array (containing at least one number) which has the largest sum.

For example, given the array [-2,1,-3,4,-1,2,1,-5,4],
the contiguous subarray [4,-1,2,1] has the largest sum = 6.

动态规划思路，d[i]为到以i结尾的子串的最大值，到i+1时，如果d[i] <= 0，d[i+1] = arr[i+1]，否则d[i+1] = d[i] +arr[i+1]。发现每次计算只与前一个状态有关，那么久可以只设一个变量存放之前的结果。

public class Solution {
    public int maxSubArray(int[] nums) {
        if(nums.length ==0 || nums==null) return Integer.MIN_VALUE;
        int pre = nums[0];
        int res = nums[0];
        for(int i = 1; i < nums.length; i++){
            if(pre > 0){
                pre += nums[i];
            }else{
                pre = nums[i];
            }
            res = Math.max(res, pre);
        }
        return res;
    }
}

Top的方法思路也是如此，不过有一些还是开了一个数组，不值得。